The present invention relates to electrically conducting printable webs of plastic, processes for the preparation of electrically conducting printable webs of plastic, and a binder by means of which electrically conducting organic polymers can be applied to plastic sheets.
For reasons of explosion protection and electromagnetic shielding and due to the increased demand for electroluminescent displays, LCDs and touch screens, electrically conducting surfaces are increasingly gaining importance because they can prevent electrostatic charging. The focus of interest is shifting more and more to electrically conducting plastic surfaces.
The conventionally used plastics have a high resistance which may be in the range of 1015 Ohm/xe2x96xa1. In order to increase the conductivity of plastics, especially of plastic sheets, metallic screen printing inks, carbon paints or wire gauze are used. However, if transparent surfaces are required, this is not possible since the surface would be no longer transparent eventually.
Therefore, to prepare transparent, electrically conducting surfaces, plastic sheets are sputtered with metal oxide layers in an expensive process under ultrahigh vacuum. Usually, indium tin oxide (ITO) is used for this purpose.
However, these sputtered layers cannot be printed afterwards since the printing inks fail to adhere to the metal oxide layer satisfactorily. On the other hand, if layers already printed are to be sputtered, there is a risk that volatile components of the printing inks are vaporized in the ultrahigh vacuum necessary for sputtering.
Due to the use of ultrahigh vacuum, sputtering processes are very expensive. Further, sputtered layers exhibit a change in resistance upon mechanical and/or thermal deformation of the surface.
The use of the heavy metal oxides in sputtered layers involves a danger for humans and the environment both in production and in application.
The object of the invention has been to provide electrically conductive plastic surfaces which can be printed on with a particularly good adhesion and have improved surface properties, and processes for the preparation of such plastic surfaces in which the use of ultrahigh vacuum and heavy metals is eliminated.
Surprisingly, the object of the invention is achieved by electrically conducting printable webs of plastic having the features of claim 1, by preferred embodiments according to claims 2 to 6, electrically conducting printed webs according to claim 7, a preparation process according to claim 9, and the use of the electrically conducting printable webs of plastic according to claim 14. Claims 10 to 13 are preferred embodiments of the process.
The electrically conducting printable webs of plastic according to the invention have upper and lower sides, at least one of said sides being provided with a primer layer for printing pretreatment, comprising a substance selected from the group consisting of polyurethanes, acrylates, polyester resins with isocyanates or combinations thereof, on which another layer containing an electrically conducting organic polymer is coated.
These plastic webs are advantageous, in particular, when an electrically conducting surface is needed for reasons of explosion protection or electromagnetic shielding, or for printing with electroluminescent pastes. In addition, these plastic webs do not exhibit a significant change in resistivity upon being deformed.
Preferably, the plastic webs are made of polyethylene, polycarbonate, polyacrylate, polyester, polypropylene, poly(vinyl chloride) or copolymers thereof.
The primer layer for the electrically conducting printable webs of plastic are formed by a primer made of polyurethanes, acrylates, polyester resins with isocyanates. Particularly preferred components of the primer are acrylate copolymers of the Neocryl series of Polyvinyl-Chemie Holland N.V. (Neocryl XK90, XK11, BT26, A-1052), Halloflex 202 available from ICI (vinyl acrylate copolymer), Neopac E-130 (polyurethane-acrylic copolymer), Viclan VL805 (PVDC), Dynapol L206 (polyester), Elecond PQ50B (acrylate), Alberdingk APU1060 and U910 (polyethylene-polyurethane copolymers), Saran F-310 (PVDC), Alberdingk APU1014, Aquacote 287/4 (styrene acrylate), Neorez R-970, R-973, R-974, R-986, R-940, R-972, optionally together with Xama (tris(N-aceridinyl)ethane), poly(oxy-p-phenylenesulfonyl-p-phenylene) of the PES series available from Deutsche ICI GmbH (PES 2000, PES 124G, PES 124S, PES 215G), Vylon 103, Vylon 240, Pioloform BL 18, PolyDisB/300LF, Plexigum M890, Vital PE-2200, Ucar Vinyl VMCH, Melinex 525, NeocXK11, NeocA1052, Cariflex TR1102, Clarene R-20 and Clarene L-6. The primer layer serves as a printing pretreatment and mediates the adhesion of the inks, paints, pastes or the like, applicable by various printing methods, which would otherwise perhaps not exhibit sufficient adhesion on the plastic webs, especially when deformed.
In this connection, a good adhesion means that the printed electrically conducting webs of plastic according to the invention will achieve a GT value of between 0 and 3, preferably between 0 and 2, especially between 0 and 1, in a cross-hatch adhesion test according to DIN 53 151 or ASTM D 3002 or ASTM D 3359.
The GT value indicates how strongly a printed structure or the like adheres to the surface. GT values are a measure for the adhesion of the printed structure to the surface and range from 0 to 5. A value of 5 indicates that an almost complete removal of the printed structure has occurred in the test whereas a GT value of 0 means that no printed structure has been removed. Thus, low GT values mean a good adhesion of the printed structure to the surface.
As said electrically conducting organic polymer, there are used, in particular, polyamidines, polyacetylenes, polypyrroles, polythiophenes, free-radical containing salts and combinations thereof. Suitable materials include N-n-propyl-iquinolinium, available as OS-CON from Sanyo (Japan), polyanilines available under the designation Incoblend from Zipperling-Kessler (Germany), polythiophenes available under the trade name Hostaphan RN 12 from Hoechst (Germany), polyanilines available under the designation CP EX-1 available from Hexcel (USA), and the products of Ciba-Geigy (Switzerland) available under the designation TEC.
xe2x80x9cFree-radical containing saltsxe2x80x9d means those compounds, in particular, in which a plastic material has been converted to a free-radical containing state by doping, for example, with Br2 or I2.
The layer containing the electrically conducting organic polymer optionally contains a binder whereby the adhesion to the primer layer can be improved. In particular, the ratio of electrically conducting organic polymer to binder can be varied in such a way, that besides very small resistances, resistances in the range around 106 Ohm/xe2x96xa1 having antistatic properties can also be achieved.
It is advantageous to use transparent polymers because mechanically and thermally deformable, transparent, printable, electrically conducting plastic webs are thus obtained which have not been available to date in this form.
It is particularly advantageous to use the plastic web according to the invention in the fields where transparency of the plastic surface is necessary, for example, as a display in electronic equipment.
These printable webs of plastic can be printed or coated with, for example, printing inks, paints, hard lacquers, electroluminescent screen printing pastes or liquid crystals. In addition, the printing and/or coating can be effected on both sides irrespective of whether the layer containing the electrically conducting organic polymer is applied on one or both sides.
As the binders for applying the electrically conducting organic polymer, artificial resins or artificial-resin-like substances, such as poly(vinyl chloride) latexes, poly(methyl methacrylate) latexes, polyurethane dispersion, poly(vinyl acetate) or poly(vinyl alcohol), are particularly suitable.
The process according to the invention for the preparation of electrically conducting printable webs of plastic involves the application of a primer to form a primer layer for printing pretreatment, and the application of another layer containing an electrically conducting organic polymer.
The process is characterized, in particular, by the application of the conductive coating under normal pressure and by the avoidance of heavy metals.
Particularly suitable are methods in which the primers forming the primer layer are applied by coating techniques such as reverse roll, knife or gravure coating.
For applying the conductive organic polymer, in particular, aqueous or organic solutions or mixtures thereof are suitable, wherein alcohols, ketones, heterocycles or combinations thereof, in particular, are suitable as solvents for the solution. Optionally, the polymer is applied together with a binder.
The structure of the plastic web according to the invention and its preparation are illustrated in the following Examples.